1. Field of the Invention
This invention concerns the generation and monitoring of video signal waveforms, such as those produced by camera apparatus in a broadcast environment, for example.
2. Description of the Related Art
Waveform monitors have been employed in television production environments for some time, so as to allow monitoring of the level of video signals with respect to time. Typically, waveform monitors are used by engineers to assist in calibration of video cameras, so as to match exposure, white balance and contrast etc. They may also be used in the installation and diagnostics of equipment in a broadcast environment, such as a television studio.
Analog waveform monitors are similar in construction to oscilloscopes, in that an electron beam in a cathode ray tube-type display is swept across the display, the display having phosphors deposited thereon. The magnitude of an input video signal from a device under test controls the vertical position of the electron beam during its sweep, with horizontal and vertical synchronization pulses controlling the electron beam's horizontal position. This allows the level of the video signal to be monitored. As will be appreciated by those skilled in the art, the phosphors glow at a degree determined by the instances of the electron beam exciting the phosphors at a particular position on screen, up to the point at which the phosphors saturate. Thus, repetitive signals appear brighter due to repeated illumination of phosphor by the electron beam. Additionally, the phosphorescence of the display exhibits persistence, which is to say there is a non-instantaneous decay to the brightness of the phosphor following illumination by the electron beam, thereby providing an opportunity to compare new data with old. This is particularly useful as it makes identifying an intermittent, anomalous signal component in an otherwise repetitive signal possible for an engineer.
More recently, digital waveform monitors have begun to be more commonly used, as they allow the inclusion of more features and capabilities, such as vectorscope display, eye pattern, jitter display and the like. Digitization of the input video signal is performed, followed by a degree of digital signal processing, possibly using field-programmable gate arrays. Such waveform monitors tend to use displays segmented into pixels, with a rasterizer being present to convert a video signal such that it is suitable for display. Given the fact that it is desirable to package digital waveform monitors into smaller formats, displays tend to be based on flat-panel technologies such as liquid crystal displays. Such display types do not exhibit the persistence of the phosphor coating used in cathode ray tube-type displays.
Thus, whilst there is increased sophistication in terms of the signal processing features available in modern digital devices over their analog predecessors, there are still some familiar characteristics of analog waveform monitors that it is desirable to emulate, such as the aforementioned phosphor persistence. Further, manufacturers are no less concerned with reducing power consumption, instrument complexity and component costs despite the move to a digital processing environment, therefore necessitating innovative approaches to providing the degree of processing required despite limited hardware capability.